This is an small bug. You can place decorations on bushes then remove the decoratation on it fast. You will have a small amount of time until it returns but in that time you can build something on it.
Exampled in pictures (5)
http://img838.imageshack.us/img838/2784/bug1x.png
http://img845.imageshack.us/img845/2776/bug2r.png
http://img641.imageshack.us/img641/6191/bug3o.png
http://img191.imageshack.us/img191/7839/bug4x.png
http://img19.imageshack.us/img19/6936/bug5e.png
